Technical Abstract:
The incorporation of biochar into soils has been shown to increase soil retention of nutrients, heavy metals, and organic contaminants. Recent research has suggested that biochar may also be effective in limiting the transport of bacteria through soils. This study aimed to evaluate the effects of biochar feedstock type, pyrolysis temperature and rate of biochar amendment on soil retention of Escherichia coli under water-saturated and unsaturated conditions. We conducted column experiments to compare how biochar produced from two feedstocks - poultry litter and pine chip - and pyrolyzed at two different temperatures - 350 and 700 'C - affects bacterial transport through a water-saturated and partially saturated (~50% of saturation) fine sand when applied at rates of 1 and 2 % (w/w). Two E. coli isolates with contrasting surface properties were used in the study. Increasing the rate of biochar addition and the use of biochar pyrolyzed at 700oC led to lower E. coli fractional recoveries (fr). Pine chip biochars proved more effective in limiting transport of both isolates reducing fr by as much as 5 orders-of-magnitude. Addition of poultry litter biochar pyrolyzed at 700oC also significantly reduced fr while mixing poultry litter biochar pyrolyzed at 350oC enhanced transport. For all treatments, we found that the effectiveness of biochar amendments increase under unsaturated conditions. Our results show that the addition of biochar can affect the retention and transport behavior of E. coli through a sandy soil and that feedstock type, biochar application rate, biochar pyrolysis temperature, bacterial surface characteristics, and the degree of saturation were all important factors determining the transport of E. coli through our test soil.